The Denver school board met yesterday to discuss the issues surrounding the Challenges, Choices and Images Charter School, which serves about 600 students in northeast Denver. The school has until Thursday to submit an improvement plan. Eleven employees have been accused of crimes, including an assistant principal buying crack, a teacher who physically abused his girlfriend, and a security guard who solicited a prostitute. Because charters do not have as stringent hiring practices as traditional public schools, teachers with past misdemeanors may be hired.